1. Field of the Invention
The present invention relates to a rotor of a rotary electric machine, which rotor includes a rotor core, and a permanent magnet embedded near an outer periphery of the rotor core.
2. Description of Related Art
In a permanent magnet synchronous rotary electric machine configured such that a permanent magnet is embedded in a rotor core, when a rotor heats up along with driving of the rotary electric machine, not only magnet performance decreases to decrease torque and efficiency, but also demagnetization of the permanent magnet occurs due to high temperature. If a magnet having a high coercive force is employed, a problem with demagnetization can be avoided. However, in this case, it is necessary to increase a content of heavy rare earth, which causes an increase in cost.
In view of this, in order to cool down the rotary electric machine, various structures have been suggested conventionally. For example, Japanese Patent Application Publication No. 2006-067777 (JP 2006-067777 A) describes a technique in which oil supplied from a supply oil passage formed inside a rotating shaft is discharged through a plurality of cooling oil passages formed inside a rotor core, so as to cool down a rotor. In JP 2006-067777 A, the cooling oil passage extends on a d-axis of a rotary electric machine. The cooling oil passage extending on one d-axis may be constituted by one slot extending on the d-axis from an inner peripheral end of one electromagnetic steel sheet to an outer peripheral end thereof. Alternatively, the cooling oil passage extending on one d-axis may be constituted by a plurality of slots respectively formed on a plurality of electromagnetic steel sheets arranged consecutively, which slots are arranged in respective radial ranges displaced from each other. Further, a similar technique is described in Japanese Patent Application Publication No. 2008-228523 (JP 2008-228523 A).
Further, Japanese Patent Application Publication No. 2008-228522 (JP 2008-228522 A) also describes a technique in which oil supplied from a supply oil passage formed inside a rotating shaft is discharged through a plurality of cooling oil passages formed inside a rotor core, so as to cool down a rotor. In JP 2008-228522 A, a slot extending on a q-axis of a rotary electric machine is formed on each of a plurality of electromagnetic steel sheets arranged consecutively, so that the slots are arranged in respective radial ranges displaced from each other, thereby forming a cooling oil passage extending on the q-axis.
In the meantime, as generally known, a permanent magnet synchronous rotary electric machine uses a reluctance torque other than a magnet torque of a permanent magnet. In order to secure a large magnet torque, it is necessary to secure a d-axis magnetic path that crosses a q-axis. Further, in order to secure a large reluctance torque, it is necessary to secure a q-axis magnetic path that crosses a d-axis.
However, in the conventional techniques described in JP 2006-067777 and JP 2008-228523 A, a slit functioning as a refrigerant oil passage is formed in a middle of the q-axis magnetic path, so that the slit serves as an air gap of the magnetic path, which causes a decrease in the reluctance torque. Further, in the technique of JP 2008-228522 A, a slit functioning as a refrigerant passage is formed in a middle of the d-axis magnetic path, so that the slit serves as an air gap of the magnetic path, which causes a decrease in the magnet torque.